ISOZYME VARIATION IN TEN NATURAL POPULATIONS OF Pinus greggii ENGELM

Abstract

In order to know the level of genetic variation of Pinus greggii Engelm., 16 loci from eight enzyme systems were analyzed on the megagametophyte tissue of seeds from 128 trees sampled in 10 natural populations of P. greggii throughout the range of the species; a sample of six seeds from each tree was used. The parameters of genetic diversity estimated for each population were the percentage of polymorphic loci, the average number of alleles per locus and the observed and expected heterozigosities. Most populations showed a strong trend towards allele fixation, with less than 45 % of polymorphic loci and 1.5 alleles per locus on average for all populations. However, in some populations the percentage of polymorphic loci and the number of alleles per locus were as high as 60 % and 1.8, respectively. Despite the low level of variation found and the small size of most populations, the average observed heterozigosity (Ho=0.21) was slightly higher than the expected heterozigosity (He=0.17) in eight populations.